Despite the fact that Global System for Mobile communication (GSM) networks have been commercially deployed for almost two decades, interest on the continued improvement of the GSM/EDGE (Enhanced Data for GSM Evolution) technology has not dwindled. Network equipment manufacturers, mobile equipment manufacturers and telecom operators continue to be keen on developing further the GSM system. Improvements to the hardware and spectral efficiencies for both voice and packet data services are being actively sought.
The slot format used for normal bursts in GSM, GPRS (General Packet Radio Service), enhanced GPRS (EGPRS) and EGPRS2A is illustrated in FIG. 1, as specified in “3GPP TS 45.001, “Physical layer on the radio path” Technical Specification Group GSM/EDGE Radio Access Network; 3rd Generation Partnership Project”. Here, the description is based on samples at rate Fs=13000/48≈270.83 kHz, which also is the normal symbol rate within a slot. The slot format is built out of 148 symbols with 3 tail symbols, 58 encoded data symbols, 26 training sequence symbols, 58 encoded data symbols, and finally 3 tail symbols. A guard of 825 samples is introduced to separate adjacent time slots. Eight such slots are placed sequentially in time constructing a TDMA frame see “3GPP TS 45.001, “Physical layer on the radio path” Technical Specification Group GSM/EDGE Radio Access Network; 3rd Generation Partnership Project”. One user may be allocated one or several of these slots within a TDMA frame.
A training sequence is a sequence known to the receiver. This is inserted into the slot such that the receiver may estimate distortions of the received signal after it is transmitted. The receiver may then compensate for these distortions such that the reliability of the communication is increased. Examples of distortions which may be estimated by help of the training sequence are                Transmitter and receiver filters impulse responses        Radio channel impulse response        Timing offset        Noise variance        Noise correlations between antennas (in receivers with multiple antenna branches)        Carrier frequency offset        
The training sequence may also be used in order to do blind detection of used modulation.
With the use of wireless packet data communication, the need for higher peak rate and higher spectral efficiency is increasing. Especially, the need for higher bit rates at low to medium signal to interference and noise ratios (SINR) are wanted. This results in the need for alternative slot formats which are robust without sacrificing high peak rate for high SINR.
The slot formats in Third Generation Partnership Project (3GPP) technical specification TS 45.001 with the modulation (as specified in “3GPP TS 45.004, “Modulation” Technical Specification Group GSM/EDGE Radio Access Network; 3rd Generation Partnership Project, (Release 1999)”, incorporated herein by reference), and transmitter filter (as specified also in 3GPP TS 45.004), result in a received signal with inter-symbol-interference (ISI). The physical radio channel further increases the amount of ISI. As a result, the receiver has to rely on advanced algorithms in order to detect transmitted symbols and recover the transmitted bit sequence. The received signal is further distorted by transmitter and receiver imperfections (resulting in e.g. phase noise), carrier frequency offset, timing errors, co-channel and adjacent channel interference etc.
Hence robust receiver algorithms are needed for alternative slots formats based on Zero padding or Cyclic Prefix.